A light bulb is connected in the circuit shown in the figure with the switch S open and the capacitor uncharged.The battery has no appreciable internal resistance.Which one of the following graphs best describes the brightness B of the bulb as a function of time t after closing the switch?
A)1
B)2
C)3
D)4

Question

A light bulb is connected in the circuit shown in the figure with the switch S open and the capacitor uncharged.The battery has no appreciable internal resistance.Which one of the following graphs best describes the brightness B of the bulb as a function of time t after closing the switch?  
A)1 
B)2 
C)3 
D)4

Quizplus · Accepted Answer

When the switch is closed, the capacitor begins to charge up and the potential difference across the capacitor decreases. As a result, the potential difference across the bulb also decreases, and its brightness decreases accordingly. At first, the bulb is very bright because the potential difference across it is equal to the emf of the battery. As time goes by, the potential difference across the capacitor builds up, reducing the potential difference across the bulb. Graph 2 shows this behavior correctly, with the brightness of the bulb decreasing over time as the capacitor charges up. The other graphs do not show this behavior accurately.

A Light Bulb Is Connected in the Circuit Shown in the Figure